Human allograft dermal tissue has been widely accepted for use in various surgical procedures for decades. For example, acellular dermal matrices (“ACDMs”) derived from allograft dermal tissue are used in the repair of ventral abdominal hernias and other abdominal wall defects. Commercially available ACDMs include FlexHD® Structural™ ACDM, which is marketed by Musculoskeletal Transplant Foundation (Edison, N.J.), as well as AlloDerm® ACDM and AlloDerm® Ready to Use (“RTU”) ACDM, both of which are marketed by LifeCell Corporation (Branchburg, N.J.). The nature of the dermal tissue from which these ACDMs are derived is explained with reference to FIG. 1, which illustrates the microstructure of human skin.
Human allograft skin, as illustrated in FIG. 1, is recovered from either live or deceased donors after receiving consent from the individual donor or donor's family. The skin is made of several layer-like components, including the outer-most epidermis E, and the dermis D, which lies beneath the epidermis. The hypodermis H (also referred to as the subcutis) lies beneath the dermis D, but is not part of the skin. Rather, the hypodermis H contains adipose and muscle tissue. The dermis D itself includes the papillary dermis PD, which lies adjacent the epidermis E, and the reticular dermis RD, which lies between the papillary dermis PD and the hypodermis H. The papillary-reticular dermis interface PRI, lies between the papillary dermis PD and the reticular dermis RD. The dermis-epidermis junction (“the DEJ”) lies between the papillary dermis PD and epidermis E.
The process for deriving the foregoing ACDMs from dermal tissue involves removing the the epidermis E (e.g., by a chemical process that causes the epidermis to slough off), and thereby exposing the DEJ that was adjacent the epidermis E. Beneath the DEJ lies the papillary dermis PD, the papillary-reticular dermal interface PRI, and the reticular dermis RD. The dermal tissue that is recovered for the ACDMs may therefore include the DEJ, papillary dermis PD and at least part of the reticular dermis RD. The recovered dermal tissue is decellularized and aseptically processed to meet sterility testing requirements.
The foregoing ACDMs are derived from recovered tissue that includes the entire papillary dermis PD. The microstructure of the papillary dermis PD is not uniform. More particularly, the papillary dermis PD has an upper portion, or side, that was immediately adjacent the DEJ and therefore closer to the epidermis E (i.e., “the epidermal portion”), and a structurally different lower portion, or side, that was farther from the DEJ and epidermis E, and adjacent the deeper reticular dermis RD (i.e., “the dermal portion”). The epidermal portion of the papillary dermis PD contains a more densely-packed collagen matrix than the relatively more open collagen matrix contained in the dermal portion. As such, the dermal portion is more porous than the epidermal portion. This dual structure is also a property of the foregoing ACDMs, and is ideal for repairing ventral abdominal hernias and other abdominal wall defects, as the more densely-packed epidermal portion of the ACDM (i.e., incorporating the epidermal portion of the papillary dermis PD) possesses the tensile strength and stiffness required for such load-bearing tissue repairs, and the more porous dermal portion of the ACDM (i.e., incorporating the dermal portion of the papillary dermis PD, as well as at least a portion of the loosely-packed and porous underlying reticular dermis RD) provides an open collagen structure that promotes vascularization, cellular attachment and tissue ingrowth. Nevertheless, this dual structure, which may only be visible on a microscopic scale, presents concerns about identifying and maintaining the side orientation of the ACDM, i.e., during a surgical procedure.
Allograft dermal tissue-derived ACDMs have also been used in plastic surgery procedures, including breast reconstruction, where the ACDM is implanted to function as an internal sling that is draped around a breast implant and/or tissue expander. While the high tensile strength and stiffness of the foregoing ACDMs are important for hernia and abdominal wall repairs, breast reconstruction and other plastic surgery procedures do not involve the load-bearing and other tissue considerations inherent in hernia and abdominal wall repairs. Instead, materials used as slings and similar devices in breast reconstruction should possess biomechanical properties that are well-suited to such applications, including predictable suppleness, flexibility and uniform pliability sufficient for such slings to stretch and expand without tearing during tissue expansion (i.e., using breast implant and/or tissue expander). Ideal materials for breast reconstruction and other plastic surgery procedures should also possess sufficient tensile strength, preclude suture tear-out, both during implantation and expansion through the post-operative phase, and allow rapid and efficient cellular ingrowth equally from either side of the ACDM.